Parity doubling of nucleons and Delta baryons across the deconfinement phase transition

TL;DR

This study uses lattice QCD to investigate how nucleon and delta baryon parity partners become degenerate across the deconfinement transition, providing evidence of chiral symmetry restoration at high temperatures.

Contribution

It presents the first lattice QCD analysis of parity doubling in nucleon and delta baryons across the deconfinement phase transition, using advanced spectral analysis methods.

Findings

Clear in-medium effects observed in the hadronic phase.

Parity doubling evident in the quark-gluon plasma phase.

Negative-parity ground states show significant medium modifications.

Abstract

At zero temperature the negative-parity ground states of the nucleon and delta baryons are non-degenerate with the positive-parity partners due to spontaneous breaking of chiral symmetry. However, chiral symmetry is expected to be restored at sufficiently high temperature, in particular when going from the hadronic to the quark-gluon plasma (QGP) phase. This would imply that channels with opposite parity become degenerate. We study the nucleon (spin $1/2$) and $\Delta$ (spin $3/2$) baryons in both parity sectors using lattice QCD. The range of temperatures spans both the hadronic and QGP phases. Using the FASTSUM anisotropic $N_f = 2 + 1$ ensembles, we analyze the correlation functions and the spectral functions using respectively exponential fits and the Maximum Entropy Method. We find clear evidence of in-medium effects in the hadronic phase, especially for the negative-parity ground state, and of parity doubling in the QGP phase.